Messenger - Vol. 1, No. 3, Page 8
Spring 1992
After while, crocodile...
A newly discovered fossil bed dating back some 17 or 18 million
years provides proof that Delaware was once inhabited by crocodiles
and small horses no bigger than Irish setters.
The Miocene era fossils were discovered last fall when Scott
Andres of the Delaware Geological Survey, housed at the University,
visited a sand pit being dug near Garrison's Lake by contractors for
the Delaware Department of Transportation (DelDOT). Evidence of
prolific marine life--fossilized clams, oysters and snails--was found
five feet below present sea level. By the time the pit reached 20 feet
below, teeth and bones of vertebrates ranging from crocodiles and
rhinoceroses to sharks and whales were unearthed.
"It's hard to find fossil beds in Delaware," says Kelvin W.
Ramsey, associate scientist with the survey. "The state is generally
flat so we don't have deep highway road cuts, and the water table is
so high we usually don't have deep excavations. This excavation, which
was providing road fill for the new relief route, went unusually deep.
Now, it's about 25 feet below sea level."
Many types of teeth have been found, Ramsey said, because they
are the hardest bones and most easily preserved. Geologists have
identified nine different types of shark teeth, grinding teeth from a
cow-nose stingray, tiny teeth from coral-grazing fish, at least one
tooth from an ancient crocodile and the horse teeth.
Although fossil evidence indicates that most animals inhabiting
Delaware during the Miocene era would be recognizable today, some-like
the horse and the whale-were smaller and still others are now extinct.
"Bones were found that are possibly part of a chalicothere, a strange,
horse-like animal with claws on its feet," Ramsey says. "On the other
hand, we've identified oysters of the same species that now lives in
Delaware Bay.
"This is the earliest known occurrence of these oysters, so
Delaware can be called the birthplace of the edible oyster," he adds.
Ramsey speculates that the climate of Delaware was warmer 17
million years ago, probably similar to that of northern Florida or
southern Georgia. The Atlantic Coast reached about 50 miles further
inland than it does today, and shrubby trees and palms grew close to
the shifting shoreline. Because grasses had not developed yet, the
small horses, rhinos and the chalicotheres probably browsed on the
trees much as deer do today, he says.
Fossils of both land and marine species are mingled in one site
because storms and floods carried the remains of land animals
downriver into the ocean, he points out.
Several staff members of the Smithsonian Institution are working
on the vertebrate remains to better determine the geology of the site,
Ramsey says. And Lauck Ward of the Virginia Museum of Natural History
is studying the shells. "In fact, the Smithsonian researchers are
particularly excited about the diversity of mammal remains. This may
well provide the best collection of Miocene mammal fossils on the East
Coast of the United States," he says.
Microfossils of protozoa, such as radiolaria and foraminifera,
are being examined carefully by Richard Benson of the survey because
these creatures are found world-wide in deep seas and so can be used
to date the site with a small time frame, he adds.
Important as a significant Miocene fossil find in Delaware, the
site is also of interest to geologists because it is part of the
Cheswold aquifer, a subsurface zone that provides drinking water for
the towns of Cheswold and Dover. "It's rare to actually get our hands
on an aquifer," Ramsey says. "Normally, we just see records from a
well driller or a core sample. This site will help us understand where
the aquifer is located in the subsurface and how water is stored and
moves through the aquifer.
"We have a short window of opportunity to study these sands and
collect specimens because ultimately the site will be graded over and
water will be allowed to return to normal levels."
University geologists have gained a little extra time to look for
rare fossils, however. DelDOT has delivered three truckloads of sand
from the site for the scientists to sift through.
-Cornelia Weil